Stents are placed within a blood vessel for treating stenoses, or strictures. They are implanted to reinforce collapsing, partially occluded, or weakened blood vessels. More generally, however, stents can be used inside the lumina of any physiological conduit including arteries, veins, vessels, the biliary tree, the urinary tract, the tracheobronchial tree, the urinary system, and the cerebral aqueduct.
Typically, a stent will have an unexpanded diameter for delivery to a treatment site and an expanded diameter after placement in the vessel or the duct. Some stents are self-expanding and others are expanded mechanically with a radial outward expansion force provided from within the stent, as by inflating a balloon. Whether self-expanding or mechanically expanded, the stents expand until there is an equilibrium between the compressive strength (the force required to collapse a stent) and the expansion force. A high expansion force must therefore be generated in order to provide a high compressive strength. While it is possible to generate a high expansion force with a mechanical expansion device like a balloon, some self-expanding stents have a reduced expansion force and therefore low compressive strength. Further, stents which are mechanically expanded must provide space within the interior of the stent in which the expanding device may be placed and thus a larger delivery profile is required.
Prior art stents which provide a high compressive strength and low expansion force have used sheets of material which are rolled into themselves and when rolled have a discontinuous circumference. These stents employ a locking mechanism which locks when the stent is unrolled. While these prior art locking stents provide a high compression strength and low expansion force, they can not be rolled into a profile small enough to make them practical for delivery. It is therefor desirable to provide a stent with the combination of as small an expansion force as possible, as high a compressive force as possible, and as small a delivery profile as possible.